1. Technical Field of the Invention
The invention relates to spin-stabilized missiles and methods for spinning missiles to stabilize them. Particularly, the invention relates to missiles and methods utilizing thrust to impart spin or roll.
2. Description of the Prior Art
One problem in accurately targeting missiles is the possibility of thrust misalignments relative to the missile center line. Such misalignments may result in undesirable trajectory excursions during the boost phase when the rocket is firing. One way of maintaining desired accuracy, particularly when engaging targets at minimum range, is by rolling or spinning the missile so that the misaligned thrust does not dwell for an excessive amount of time in any one roll quadrant. The roll rates required to avoid unacceptable deviations in trajectory can be significant. In an exemplary simulation, a thrust misalignment of 0.1xc2x0 was found to create unacceptable flight path deviations with missile roll rates of less than 15 Hertz.
One method of imparting a spin or roll rate to a missile has been through use of aerodynamic forces generated by canted fins on the missile. One serious shortcoming of this approach stems from the fact that the torque applied by the fins is a function of the forward velocity of the missile. Upon launch, missile velocity is low, resulting in correspondingly low aerodynamic stability of the missile. This immediate post-launch period is therefore the time when the missile is most affected by thrust misalignments. Conversely, the magnitude with which the thrust misalignment acts on the air frame is a function of the thrust profile and nozzle asymmetry. The thrust misalignment is nearly independent of missile velocity. By virtue of the low launch velocity, aerodynamic rolling forces generated by canted fins start out very low and increase as the missile builds speed. This results in a very low roll rate early in the flight when the missile is most susceptible to thrust misalignment. The spin or roll rate increases as the missile goes down range, but the minimum required roll rate may not be achieved until the missile has flown a considerable distance and has suffered a considerable deviation from the desired trajectory.
Another method of imparting a roll rate to a missile has been to utilize spiral grooves in the launch tube, much like rifling is used to impart spin to a bullet as it travels the length of a gun barrel. This technique has the potential for imparting a substantial roll rate at low velocity. However, it has the disadvantage that it may apply high mechanical drag forces to the missile as it moves through the launcher.
Yet another method of imparting spin to a missile has been to employ turning vanes to the main rocket motor nozzle as a means of imparting rolling torque to the missile air frame. This method may impart substantial roll rates at low velocities. Nevertheless, it adds undesirable weight, complexity, and cost to the nozzle design. It also may reduce nozzle efficiency. Furthermore, it may contribute to thrust misalignment due to asymmetric erosion of the turning vanes.
From the foregoing it may be seen that a need exists for spin-stabilized missiles and methods for imparting spin to missiles that avoid the disadvantages of the prior methods.
A spin-stabilized missile includes two or more spin nozzles along a perimeter of the missile, the nozzles being operatively coupled to a pressurized gas source. The pressurized gas source provides pressurized gas which passes through the nozzles and external to the missile, thereby providing circumferential thrust which causes a torque on the missile that results in the missile rolling or spinning. The pressurized gas source may be a pressure container containing solid rocket fuel. The pressurized gas source for spinning the missile may be the same as that for the missile""s main propulsion system.
According to an aspect of the invention, a missile includes nozzles tangentially mounted on a missile surface, the nozzles used to spin or roll the missile.
According to yet another aspect of the invention, a missile includes nozzles mounted flush along a perimeter of the missile, the nozzles used to impart a spin or roll to the missile.
According to still another aspect of the invention, a missile includes a separable external spin motor for imparting spin or roll to a missile during the initial part of its flight. The spin motor is then jettisoned from the missile.
According to a further aspect of the invention, a missile includes a spin propulsion system in a middle or forward part of the missile.
According to a still further aspect of the invention, a missile includes a casing, a main propulsion system at least partially within the casing, and a spin propulsion system including nozzles operationally configured to expel a pressurized gas to produce a spinning torque on the missile, wherein the nozzles are forward of the main propulsion system.
According to another aspect of the invention, a missile includes a casing having one or more openings therethrough and a spin propulsion system which includes nozzles coupled to the openings, wherein the nozzles are operationally configured to expel a pressurized gas from a pressurized gas source therethrough, thereby producing a spinning torque on the missile.
According to yet another aspect of the invention, a method of spinning a missile during flight includes providing thrust in longitudinal direction using a main propulsion system, and providing thrust in a circumferential direction by expelling pressurized gas from the missile in a substantially circumferential direction.
According to still another aspect of the invention, a method of spinning a missile includes expelling pressurized gas from a nose-mounted spin motor section, and jettisoning the spin motor section.
According to a further aspect of the invention, a method of spinning a missile includes initiating, after the missile completely leaves a launcher, expelling pressurized gas to spin the missile.
According to a still further aspect of the invention, a method of spinning a missile includes initiating expelling pressurized gas to spin the missile, after initiation of a main propulsion system and before the missile completely leaves the launcher.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.